Since April 1, for every 100 print books Amazon.com has sold, it has sold 105 Kindle books. This includes sales of hardcover and paperback books by Amazon where there is no Kindle edition. Free Kindle books are excluded and if included would make the number even higher.

Amazon sold more than 3x as many Kindle books so far in 2011 as it did during the same period in 2010.

Less than one year after introducing the UK Kindle Store, Amazon.co.uk is now selling more Kindle books than hardcover books, even as hardcover sales continue to grow. Since April 1, Amazon.co.uk customers are purchasing Kindle books over hardcover books at a rate of more than 2 to 1.

There have been signs and portents that the traditional book is in danger of going the way of the dodo, but this is actually the first real-world indication that the end of the physical book may be coming hard upon us faster than anyone ever anticipated. This is as significant a development in the world’s cultural history as any since the mass marketing of the phonograph record in the early decades of the 20th century.